omxvideodec: fix buffer leak when eglimage setup fails
omxvideodec: fix buffer leak when eglimage setup fails

Can happen if gst_buffer_pool_acquire_buffer succeeds but
gst_buffer_n_memory (buffer) is not exactly 1.

In theory this should not happen because the decoder requests
EGLImage(RGBA) but better to fix any leak on corner cases.

https://bugzilla.gnome.org/show_bug.cgi?id=784365

GStreamer/gst-omx,GStreamer/gst-omx,CapOM/gst-omx,GStreamer/gst-omx,CapOM/gst-omx,CapOM/gst-omx